The Power of Anecdotal Evidence

In your business presentations, you may be tempted to stick to hard, proven facts and statistics to persuade your audience. But a powerful anecdote can trump objective facts.

The power of the anecdote

1. Vaccinations and autism

A recent Scientific American article by Michael Shermer “How Anecdotal Evidence can Undermine Scientific Results” discusses the medical controversy over vaccinations and autism. Many parents are convinced that their children developed autistic symptons as a result of a childhood vaccination. There is currently no scientific proof that this is so and many scientific arguments that show that it is highly unlikely. Despite that many parents continue to strongly believe in a causative link.

Michael Shermer explains:

The reason for this cognitive disconnect is that we have evolved brains that pay attention to anecdotes because false positives (believing there is a connection between A and B when there is not) are usually harmless, whereas false negatives (believing there is no connection between A and B when there is) may take you out of the gene pool. Our brains are belief engines that employ association learning to seek and find patterns.

So our brains naturally make connections from anecdotal evidence -even though there is no scientific proof.

2. Chronic causes and high-profile emergencies

Further evidence of the strength of anecdotal evidence is the struggle that charities have in funding vital ongoing work such as fighting malaria and AIDS, compared to the deluge of funds that pour in for high profile crises, such as the Asian Tsunami or Hurricane Katrina.

Here are the statistics for the estimated number of people who die each month from chronic causes:

AIDS 250,000

Famine 150,000

Malaria 80,000

Infectious diarrhea 180,000

TOTAL 660,000 deaths each month

By contrast the number of people who died in the Asian Tsunami was 280,000 and Hurricane Katrina, 1,093. When there’s a crisis, the emotional video footage and tragic stories motivate us to donate money. The sobering statistics can’t compete.

Combining statistics and anecdotes

You would think that combining statistics and an emotional anecdote would be even more powerful.

However, a fascinating experiment reported in Chip and Dan Heath’s book Made to Stick shows that mixing analytical information with an emotional anecdote may nullify the power of the anecdote. In the research at Carnegie Mellon University, George Loewenstein and his co-researchers compared the effect of three different charitable appeals for poor people in Africa:

Statistical information on the plight of people Gave $1.14

Story and photo of a 7 year old girl called Rokia Gave $2.38

Both the statistics and the story Gave $1.43

So the group who read about Rokia gave twice as much as the first group who only saw the statistics. And the third group gave only slightly more than the first.

The researchers followed up with a second experiment using the Rokia story. Before giving people the story to read, they either primed them to think analytically (had them work out a maths problem) or primed them to think emotionally (asked them to describe how they felt when they heard the word “baby”).

Primed to calculate Gave $1.26

Primed to feel Gave $2.34

An additional follow-up experiment I would be interested in would be looking at the impact of offering statistics after the emotional story. Would that lessen the amount of giving? On their blog, Chip and Dan Heath look at an example of exactly that – a video called The Girl Effect which moves from a story of a single poor girl to the statistics that she represents (I blogged about it a few days ago). Chip and Dan Heath praise what they call the micro-to-macro approach.

So if you’re combining anecdotes with statistics, ensure the anecdote comes first, then follow up with the statistics to give credibility.